How To Flatten In Ruby

In this blog post, we’ll cover how to flatten arrays in Ruby. Flattening an array means taking a nested array structure and turning it into a single, one-dimensional array. This can be especially helpful when handling complex data structures or when preparing data for certain operations.

The flatten Method

Ruby provides a built-in method called flatten for flattening arrays. This method can be called on any array object and will return a new array that is a flattened version of the original.

Let’s take a look at an example:

array = [1, [2, 3], [4, [5, 6]]]
flattened_array = array.flatten
puts flattened_array.inspect
# Output: [1, 2, 3, 4, 5, 6]

In the example above, we have an array with three elements. The second and third elements are themselves arrays. We can see that calling flatten on the original array returns a new array with all the elements in a one-dimensional structure.

The flatten! Method

If you want to modify the original array in place, you can use the flatten! method. This method will change the original array to be flattened, rather than creating a new array.

Here’s an example of using flatten!:

array = [1, [2, 3], [4, [5, 6]]]
puts array.inspect
# Output: [1, 2, 3, 4, 5, 6]

As we can see, the original array is now flattened, and we didn’t need to create a new variable to store the result.

Flattening Arrays with a Specific Level of Nesting

Sometimes, you may want to flatten an array only up to a certain level of nesting. Both the flatten and flatten! methods accept an optional argument that specifies the level of recursion to flatten.

Here’s an example using the flatten method with a specific level of nesting:

array = [1, [2, [3, 4]], [5, [6, [7]]]]
flattened_array = array.flatten(1)
puts flattened_array.inspect
# Output: [1, 2, [3, 4], 5, [6, [7]]]

In this example, we pass the value 1 as an argument to the flatten method, which means it will only flatten the first level of nesting. As a result, our output array still contains nested arrays, but only up to one level deep.

You can use the same approach with the flatten! method if you want to modify the original array up to a specific level of nesting.


In this blog post, we’ve explored how to flatten arrays in Ruby using the flatten and flatten! methods. These methods are useful when working with complex data structures or when preparing data for certain operations. By understanding how to use these methods effectively, you can better handle arrays and nested data in your Ruby programs.